Hydraulic props



July 31, 1962 R. REYNOLDS ET AL HYDRAULIC PROFS Filed Aug. 19, 19603,046,947 HYDRAULIC PRPS Reginald Reynolds and Peter Haig Stammers,Salron Walden, England, assignors to Acrow (Engineers) Limited, London,England Filed Aug. 19, 1960, Ser. No. 50,795 Claims priority,application Great Britain Aug. 21, 1959 4 Claims. (Cl. 121-46) Thisinvention relates to hydraulic props especially pit props of lthe typecomprising a ram working in a cylinder which, on operation of a pump tocause oil or other Working iluid to be forced past a valve in the -ramhead into a pressure chamber between the lower end of the ram and theclosed end of the cylinder, is extended out from the cylinder. In orderto retract such hydraulic props the iluid pressure in the pressurechamber has to be relieved and this is done by opening a release valvewhich is arranged normally to close a connection between the pressurechamber and a reservoir.

It is important that 'a hydraulic pit prop be completely under theminers control when it is being contracted for removal and re-useelsewhere. The rate at which this contraction occurs must be dependenton the root` conditions and it must be possible to arrest thecontraction at any instance. Although it may appear from theoreticalconsiderations that it is advantageous to contrive that the rate ofcontraction be varied automatically with variations in the load on theprop or when the prop is at a particular level, this is not attractiveas a practical proposition. Among the reasons for this are that the propis not suiiiciently under the control of the miner and that where as isto be expected, the load is Ibalanced or resisted by a spring, huntingbetween slow and rapid contraction is likely to occur.

A hydraulic prop in accordance with the invention incorporates a releasevalve comprising a main valve element which has a bleed passage of smallsize through it, the closure member of which bleed passage is also ofrelatively small size so that the force which has to be applied to it tounseat it against a given uid pressure is small, the main valve element`being of greater size so that the force which is to be supplied tounseat ift against the given uid pressure is relatively substantial,means being lprovided to open the main valve element and the bleedpassage closure member in such a way that the closure member is unseatedto open the bleed passage before the main valve element is unseated. Asthe force required -to perform the latter operation when the prop isunder load is substantial, the operator 'encounters a large resistanceto further movement of the opening means once the bleed has been openedand is thus given the indication, lwhich he needs, that the load isfollowing up the contraction of the prop. If the roof is holding up, theresistance to further movement of the opening means is small and theminer knows that he can open the main valve element and cause the propto collapse rapidly without danger.

The opening means preferably comprises a push rod or the equivalentwhich is caused to move down within the prop by a miner from outside theprop.

An example of an arrangement in accordance with the invention is shownin the acompanying drawing which is a section through the lower end vofa prop.

The prop comprises a cylinder in which is mounted for movement a ram 12having a head 14. In the particular example `shown here, provision ismade for low pressure pumping when the load is light and high pressurepumping when a pre-determined load is exceeded. The high pressure pistonis shown at 16 and the low pressure piston at 17. The pistons arereciprocated by a piston rod tube 18 operable from outside the prop.

Y 3.046,@47 Patented July 31, 1962 In the head 14 of the ram, there is`a passage normally v closed by a release valve comprising a main valveelement 20 having an opening 22 in its side. The member 20 has a tlange23 which is kept seated by a spring 24 and any pressure to which theworking fluid in the main pressure chamber 26 is subjected. When it isso seated, the opening 22 in the side of the member 20 is sealed.

so as to always present resistance to roof movement.

The head of the member 20 has a bleed hole 30 through it which is closedby a ball 32 subjected to the pressure of a spring 34 and the pressurein the chamber 26.

35 indicates a yield valve which allows uid to bleed from the pressurechamber 26 to a reservoir in the ram above the low pressure piston 17,if the pressure in the chamber 26 rises above a pre-determined maximum.In this way if the prop when set is subjected to very high rforces dueto a falling roof it gives or contracts slightly If the prop were rigidthere would be a danger of it snapping.

When the prop is to be contracted, the miner actuates push rods 38, 39(by means not shown such las those forming the subject of our`co-pending Application Serial No. 50,794 tiled August 19, 1960) thellatter of which rods passes down into the cavity within the valveelement 20. Lowering ot the push rod brings it into .contact with a pin40 which has ats formed on its sides so as to provide apassage throughbleed hole 30. The bottom of the pin 40 rests on the ball 32. Arelatively :light pressure causes the ball to be unseated so that theworking fluid bleeds slowly through the passage 30 around the pin 40 andthe ram descends very slowly, say at a rate of 1A; inch per second.

When the bleed has thus Ibeen opened, the push rod,

meets the Vhead lof the main valve member 20. If the prop is under load,the pressure in the chamber 26 will be `high and as it acts on `a largearea of the valve member, the force required to unseat that member willbe substantial. T'ne existence of a substantial resistance to Yfurthermovement of the push rod tells the miner that the prop is still underload and that either he must continue to contract the prop'at the lowspeed determined by the bleed or, if he wishes to contract the proprapidly, he must do so from Ea distance by means, for example, of aSylvester. It can, indeed, be contrived if desired that the means at therniners disposal for actuating the push rod when close to the prop donot allow him to cause the main valve element to be unseated as long asthe prop is under any susbtantial load say albove half a ton.

When the release valve is fully open fluid can iiow freely from thepressure chamber 26 up through the cylindrical portion of the main valveelement 20 to the chamber 42 -above the ram head. From there it ows upinside the piston rod tube 18 and lout to the reservoir 44 above the lowpressure piston 17 through orifices 46 and 4S.

lf when the prop has been contracted to some extent under the action ofthe bleedl the roof shows no tendency to fall, the load on the prop andthe pressure in the chamber 26 will lfall ott and the miner Will thenfind little resistance to opening of the main valve and Will be able tocause the prop to contract rapidly with safety.

The construction of the release valve can be varied from that shown andis `of little importance in itself. The bleed and the main passage can,if desired be separate passages instead of one being located within theother. The important thing is that the closure member or valve Velementof the main passage should have a large surface acted upon by thepressure in the main pressure chamber and that it be operable only whenthe bleed has been opened.

In the arrangement shown the bleed is provided by the passage betweenthe llats on the pin 40 and the sides of the bleed hole 30. This passagecan be considered to have an area equal to that of a hole of 3%4diameter.

` Y 3 The ball closing bleed hole Sil has a diameter of about 3/16" andthe ilange of the main valve member a diameter of about 7a".

The rate at which the prop contracts depends, of course, on the loadapplied to it. With a l@ inch diameter bleed, a load of tons can beletdown at a rate of one inch in 5 to 10 seconds.

It will be appreciated that insteadf the .bleed` passage being providedby the space btween the flats on pin 40 and the sides of hole 39,channels or grooves could be formed in the sides of the pin.

t The prop in accordance with the invention has the advantage over propsin which the full opening of the release valve is governed by the loadand is effected automatically in that there is little risk of its everhaving to be abandoned Vbecause of a falling roof. It will belappreciated that if the valve can be fully opened only when the prop isunder substantially no load, there is no way of contracting the proprapidly while it is under load and its removal can be effected only bybrute `force while it is in the V extended condition and is supportingthe roof; Whereas in a prop in accordance with the invention the minerwill normally be able to open the main closure member 20l by extending acomparatively strong force on the opening device. He will of courserealise that there is a following load and thus be able t0 tak Yappropriate precautions.

We claim:

l. A hydraulic prop comprising a cylinder, a ram slidvable in thecylinder, a pressure chamber in the cylinder below the ram head,arelease valve closing a passage through the ram head connecting thepressure chamber, said release valve comprising a main valve elementhaving a bleed passage through it and a closure member arranged normallyto close said bleed passage, the main valve element being of greatersize than said closure member so that the force which is to be appliedto unseat it against a given fluid pressure in the pressure chamber issubstantially greater than that needed to unseat said closure member,and a push rod extending down within the ram and being arranged to actirstly on said closure member to open said bleed passage and thereafteron said main valve element to open the passage connecting the pressurechamber and the reservoir.

2. A hydraulic prop as claimed in cla-im 1 in which said main valveelement has a cylindrical portion which is a sliding tit in the passagepassing through the lram head, said cylindrical portion being open atone end and closed at its other end by Va flange, said flange beingarranged to seat on said ram head to close said passage, the bleedpassage passing through the flange and connecting the pressure chamberand the interior of said cylindrical portion of the main valve element.

3. A hydraulic prop as claimed in claim 2 in which said cylindricalportion has an oritlcethrough its Ywall to allow hydraulic fluid to flowpast said cylindrical portion through the ram head from the pressurechamber to the reservoir when the main valve element is opened.

4. A hydraulic prop comprising a cylinder, a ram slidable in thecylinder, a pressure chamber in the cylinder below the ram head, arelease valve closing a passage through the ram head connecting/thepressure chamber and the reservoir, sa-id release valve comprising amain valve element having a bleed passage through it, said passage beingnormally closed by a ball, the main valve n,

element being of greater size than said =ball so that the force which isto be applied to unseat it against a given iluid pressure in thepressure cham-ber Vis substantially greater than that needed to unseatsaid closure member,

and a push rod extending down within the ram and having a pin portion atits lower end, said pin passing through a portion of said bleed passageto act on said ball to open the bleed passage, the push rod then actingon the main valve element to open the passage connecting y the pressurechamber and the reservoir.

Stelzer July 2, 17957

